Torque control apparatus for hydraulic power units



H. H. KOUNS 3,250,227

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TORQUE CONTROL APPARATUS FOR HYDRAULIC POWER UNITS Filed Aug. 9, 1963 '7Sheets-Sheet 5 INVENTOR.

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TORQUE CONTROL APPARATUS FOR HYDRAULIC POWER UNITS Filed Aug. 9, 1963 '7Sheets-Sheet 7 n2 17 122. W 12s f////// 2 in q. ENTOR.

United States Patent 3,250,227 TORQUE CONTROL APPARATUS FOR HYDRAULICPOWER UNITS Herbert H. Kouns, Camarillo, Calif., assignor to AmericanBrake Shoe Company, New York, N.Y., a corporation of Delaware Filed Aug.9, 1963, Ser. No. 301,092 9 Claims. (Cl. 103162) This invention relatesto hydraulic control apparatus for regulating the displacement ofpiston-type hydraulic power units by varying the stroke of the pistonsin response to load variations. The present apparatus as dis closedprimarily in its utility in controlling the displacement of a hydraulicpump, although the same hydraulic principles may be employed inregulating the displacement of a generally similar hydraulic motor.

The hydraulic pump, which has been selected to illustrate the principlesof the torque control apparatus comprises, in general, a rotatablecylinder barrel including a series of pistons slidably confined withinbores located within the cylinder barrel in a circle concentric to theaxis of barrel rotation. Rotary motion is imparted to the barrel by asource of power while reciprocating motion is imparted to the pistons byan'inclined cam plate, also termed a swash plate, which slidably engagesthe outer ends of the pistons. The degree of inclination of the swashplate, with reference to the axis of rotation of the barrel, determinesthe extent of the piston stroke and pump displacement.

Torque control or horsepower limiting apparatus of this general type isknown in the art and is utilized to prevent the power unit (motor orpump) from exceeding its rated horsepower. In the case of a pump of thepresent example, the torque control apparatus prevents the load orhorsepower output of the pump from exceeding the rated horsepower of themotor which drives the pump. In other words, if the pump is driven by amotor rated at a given horsepower, the output of the pump is regulatedby the torque control apparatus so that the motor is not operated aboveits rated capacity. Thus, if the pump is operating at a givendisplacement and output pressure, and is suddenly called upon (due toincreased loading of the hydraulic motor which is driven by the pump) todeliver a higher output pressure, this higher pressure at the samedisplacement and speed may overload the power motor and cause damage tothe motor and also to the hydraulic pump. However, the torque controlapparatus automatically reduces the pump displacement and in creases theoutput pressure, such that the product of pump pressure and displacementis maintained at a substantially constant predetermined value which isrelated to the capacity of the driving motor.

In the present example, the torque control apparatus of the inventionforms a part of the pump and is utilized to regulate the inclination ofthe swash plate in response to the load or back pressure against whichthe pump is acting. By way of example, the torque control apparatusresponds to back pressure in the hydraulic output passageway of the pumpto reduce the stroke of the pistons, and consequently the displacementof the pump when the back pressure reaches a predetermined value. Thisaction thus limits the amount of torque which is required to rotate thecylinder barrel while increasing the pressure from the hydraulic outputline of the pump so as to prevent overloading of the driving motor orpump.

The hydraulic pumps for which the torque control appar'atus is intendedmay be utilized as a hydraulic power source for driving the hydraulicmotors used in controlling 'ice aircraft, for driving the motors used inactuatingcertain components of machine tools, and in general, foroperating any hydraulic motor in which the load resistance mayvary'during operation.

One of the primary objectives of the present invention has been toprovide a torque control apparatus of-simplified, compact design whichis highly sensitive to changes in the back pressure developed in thepressure or output passageway of the pump.

A further objective of the invention has been to provide a torquecontrol apparatus including a pilot valve and an opposed stroke controlpiston which are disposed generally in axial alignment and housed withina single cross bore formed in the pump casing sons to simplifyconstruction of the pump casing.

In order to control the inclination of the swash plate, the plate isprovided with an actuating arm arranged to be shifted from a position ofmaximum inclination (maximum displacement) to a position of minimuminclination and displacement. The torque control apparatus, in general,comprises a pilot valve spool interposed in the cross bore at one sideof the actuating arm, combined with a stroke control piston slidablyconfined in the opposite end portion of the cross bore, such that theswinging end of the swash plate arm is interposed between the valvespool and stroke control piston. The pump casing includes a pressurepassageway providing communication between the high pressure outputpassageway of the pump and pilot valve spool. The arrangement is suchthat the spool is shifted axially toward the swash plate arm in responseto back pressure in the output passageway. A control passageway, alsoformed in the pump casing, leads from the valve spool to the outer endof the stroke control piston. As back pressure increases to apredetermined setting, and the valve spool is shifted toward the arm,fluid pressure is transmitted from the pilot valve spool to the outerend of the stroke control piston, causing the piston to shift the swashplate arm from its full stroke position toward the valve spool to ashorter stroke position.

Compression springs areinterposed between the swash plate arm and valvespool, the arrangement being such that, as the stroke control pistonshifts the arm in the direction to decrease the stroke, the compressionsprings are compressed to bias the valve spool in the oppositedirection, creating a servo-motion between the stroke control piston andvalve spool. By virtue of this action, the valve spool becomes balancedby the back pressure acting in a direction to shift it toward the armand the back pressure acting upon the stroke control piston in the opposite direction, thereby to hold the swash plate at a given inclinationin response to a given back pressure.

A further objective of the invention has been to pro vide a pilot valvestructure which may be adjusted in a convenient manner to vary thestroke of the pump, and also to simplify the construction of the pilotvalve itself.

According to this aspect of the invention, the pilot valve comprises twoconcentric sleeves confined within the cross bore of the pump casing.The outer sleeve is ported and provides communication with a highpressure passageway of the pump casing and with a control passagewayleading to the stroke control piston. The inner sleeve is adjustableaxially with respect to the outer sleeve and includes control portscommunicating with the ports of the outer sleeve. The pilot valve spoolis slidably confined within the inner sleeve and controls the admissionof hydraulic pressure from the high pressure outlet passageway to thecontrol passageway leading to the stroke control valve. The arrangementis such that axial adjustment of the inner sleeve with respect to theouter sleeve regulates the operation of the torque control apparatus,and more specifically controls the angle of inclination of the swashplate at a given back pressure, thus controlling the operation of thepump.

The various objectives and advantages of the present invention will bemore fully apparent to those skilled in the art from the followingdetailed description taken in conjunction with the drawings.

In the drawings:

FIGURE 1 is an end view of a variable displacement hydraulic pump whichis provided with the torque control apparatus of the present invention.

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1, furtherillustrating the internal construction of the pump.

FIGURE 3 is an end view similar to FIGURE 1 taken along line 3-3 ofFIGURE 2 with the upper portion of the pump removed to illustrate morefully its internal construction. 7

FIGURE 4 is a sectional view taken along line 44 of FIGURE 2, furtherillustrating the internal construction of the pump, particularly thetiltable cam or swash plate which regulates the output of the pump.

FIGURE 5 is a fragmentary sectional view taken along line 55 of FIGURE1, detailing the hydraulic torque control apparatus of the inventionwhich regulates the output of the variable displacement pump.

FIGURE 6 is a sectional view similar to FIGURE 5, further detailing thehydraulic torque control apparatus.

FIGURE 7 is an enlarged fragmentary sectional view similar to FIGURE 6,detailing the concentric sleeves and pilot valve spool of the torquecontrol apparatus.

FIGURE 8 is an enlarged cross sectional view taken along line 88 ofFIGURE 7, detailing the relief areas formed on one land of the pumpspool.

FIGURE 9 is a similar enlarged cross sectional view taken along line 99of FIGURE 7, illustrating the relief areas of another land of the spoolvalve.

FIGURE 10 is a fragmentary sectional view, generally similar to FIGURE 7and taken along line 10-10 of FIGURE 7, showing the adjustment of theinner sleeve of the control valve to increase the back pressure settingof the torque control apparatus, the valve spool being shown in thebalanced position of FIGURE 7, prior to responding to the changedsetting of the sleeve.

FIGURES 11-13 are diagrammatic views illustrating the hydraulic torquecontrol apparatus in the positions which are assumed under variousoperating conditions.

Variable displacement pump The torque control apparatus of thisinvention is illustrated in relation to a variable displacement, pistontype hydraulic pump (or motor) shown in FIGURES 1-4. In the presentdisclosure, the structure is described primarily in its utility as apump in which the torque compensating apparatus regulates the stroke ofthe pistons in response to the back pressure or load resistance imposedby a hydraulic motor which is driven by the pump. However, when utilizedas a hydraulic motor, the torque control or limiting apparatus similarlychanges the stroke of the pistons in response to the load so as toincrease the torque and reduce the speed as the load increases.Generally speaking, the pump is similar in principle to the structuredisclosed in Patents 2,696,189 and 2,699,123 and also in the pendingapplication of Cecil E. Adams et al. for Control for VariableDisplacement Pump or- Motor Serial No. 225,484, filed on September 24,1962.

As best shown in FIGURES 1 and 2, the variable displacement pump isindicated generally at 1 and the torque limiting apparatus, which isincorporated in the pump, is indicated generally at 2. In general, thepump comprises a sectional casing or body having a base section 3 and anintermediate section 4, the two sections being secured together byscrews 5. The base section includes a flange 6 adapted to be secured byscrews 7 to the mounting collar 8 of a source of power, such as anelectric motor (not shown).

A rotatable cylinder barrel, indicated generally at 9 (FIGURE 2) isjournalled within the sectional pump body and includes a skirt portion10 attached to a flange 11 of barrel 9 by a series of screws 12. Thecylinder barrel 9 is journalled for rotation in a roller bearing 13having an outer race 14 confined in the base section 3. The skirtportion 10 of the barrel 9 forms the inner race of the roller bearing,adapting the cylinder barrel 9 to be rotated by a drive shaft 15 whichis coupled to the power motor. The motor, in turn, is secured to themounting collar 8 by means of screws (not shown) the arrangement beingsuch that the cylinder barrel 9 is rotated at the same speed as themotor. The cylinder barrel 9, as explained later, includes a series ofcylindrical bores 16 spaced radially in concentric relationship to thedrive shaft 15, each cylindrical bore having a piston 17 adapted toreciprocate to response to the rotary motion of the barrel 9.

The intermediate section 4 of the pump body includes a head, indicatedgenerally at 18 (FIGURES 1 and 2). The head 18 is provided with a flange20 attached by screws 21 to the pump section 4. The head 18 includes ahydraulic fluid intake passageway 22 and a pressure outlet passageway23. The ends of these passageways are bored and tapped (not shown)toprovide connections with the pressure and return lines of thehydraulic motor or power unit (FIGURE 2) which is driven by the pump, asexplained later. In order to prevent leakage of hydraulic fluid underpressure, the upper surface of pump body section 4 includes a circulargroove 24 (FIGURES 2 and 3) in which is seated a conventional seal ring25, which is maintained under compression by the flange 20 of head 18.To provide communication with the cylindrical bores 16, the intakepassageway 22 of head 18 inc'ludes a bore 26 (FIGURE 2) communicatingwith the upper end of the rotatable cylinder barrel 8. -A similar bore27 provides communication between the upper end of barrel 8 and theoutlet passageway 23 of head 18.

Reciprocating motion is imparted tothe pistons 17 by a tiltable cam orswash plate, indicated generally at 28 (FIGURE 2). Swash plate 28 isgenerally in the form of a yoke having a circular cam surface 30. Swashplate 28 includes a pair of bearing lugs 3131 at diametrically oppositesides which are journalled upon respective trunnions 3232. Thisarrangement permits the swash plate 28 to be shifted from a neutralposition to a tilted or inclined position to regulate the stroke of thepistons 17, thereby to regulate the displacement of the pump, asexplained later. Each trunnion 32 includes a mounting plate 33 (FIGURES2 and 4) disposed to the exterior of the base section 3 of the pump bodyand secured in place by screws 34. In order to prevent leakage, a sealring 35 is seated in a groove formed in section 3 and engaged incompression under the mounting plate 33 of each trunnion 32.

The inner end of each piston 17 of cylinder barrel 9 includes a shoe 36which is in sliding engagement with the cam surface 30 of swash plate 28(FIGURE 2). It will be understood at this point, that the angle ofinclination of the cam surface 30, with reference to the axis of thedrive shaft 15, determines the stroke of the pistons 17, therebyregulating the output of the pump. As is best shown in FIGURE 2, thereis provided a ball and socket connection between the pistons 17 and therespective shoes 36. For this purpose, the inner end of each piston 17is machined to a spherical shape 39 interfitting a similar socket formedin the shoe 36. The shoe is compressed in this area so as to couple thespherical portion 39 to the shoe.

During rotation of the cylinder barrel 9 by the drive shaft 15, cylinderbarrel 9 carries the pistons 17 and their shoes 36 in a circular path,with the shoes in sliding engagement with the cam surface 38 of theswash plate 28, thus imparting reciprocating motion to the pistons. Theextent of the reciprocation is determined by the angulation of the camsurface of the swash plate 28. The shoes 36 are held in bearingengagement against the bearing surface 30 by a hold-down plate 37(FIGURE 2) which is provided with bores embracing the individual shoes36. Each shoe includes a flange 38 interposed between the hold-downplate 37 and the cam surface 30.

The hold-down plate 37 is secured to the swash plate 28 by a retainercollar 40 (FIGURE 2), which is concentrio with the drive shaft 15. Itwill be understood that the hold-down plate 37 necessarily rotates withthe cylinder barrel 9 and pistons 17. In the present example, theretainer collar 40 rotates with the cylinder barrel 9 but tilts with theswash plate 28. For this purpose, the collar 40 is journalled in theswash plate 28 upon roller bearings 49.

The drive shaft 15 includes a splined portion 29 at its inner end keyedto a coupling element 42, which is in driving connection with the motorshaft (FIGURE'Z). The opposite end of drive shaft 15 includes a similarsplined portion 43, which slida'bly interfits a bore formed in the outerportion of cylinder barrel 9. As explained later, hydraulic fluid underpressure is forced by the pistons 17 outwardly through output passageway23 during the compression stroke of the pistons, as determined by theslant or angle of swash plate 28 with reference to the axis of driveshaft 15. At the same time, fluid is drawn from a sump by way of theintake passageway 22 during the rearward or retracting stroke of thepistons. More specifically, hydraulic fluid is drawn from intakepassageway 22 into the cylinder bores 16 in one arcuate area, duringwhich the pistons 17 are being retracted, and the hydraulic fluid isexpelled under pressure during advance motion of the pistons across asecond arcuate area which communicates with the output passageway 23(FIGURE 2).

For this purpose, the outer end (FIGURE 2) of the cylinder barrel ismachined to form a flat bearing surface which is in sliding engagementwith a similar slide bearing surface formed on the head 18. In order toprevent leakage of hydraulic fluid, the cylinder barrel 9 is urged intobearing engagement'with the sealing surface of head 18 by means of acompression spring 46 having one end seated against the end of driveshaft 15, and having its opposite end seated against a washer 47 whichis secured within the bore 48 of the cylinder barrel 9.

In order to provide communication between the cylinder bores 16 and theintake passageway 22 and outlet passageway 23, each cylinder bore isprovided with a port 50 (FIGURES 2 and 3). The cylinder head 18 includesan arcuate intake passageway 51 (shown in broken lines in FIGURE 3) andan arcuate outlet passageway 52, also shown in broken line in FIGURE 3.Thearcuate passageways 51 and 52 are concentric with the axis of shaft15 and communicate with the ports 50 of the cylinder bores 16. Thepassageways 51 and 52 communicate respectively with the intakepassageway 22 and output passageway 23 by way of the bores 26 and 27, asdescribed earlier. Briefly therefore, during rotation of the cylinderbarrel 9, the pistons 17 retract as their ports 50 traverse the arcuateintake slot 51 and advance as they traverse the arcuate outlet slot 52.

As shown diagrammatically in FIGURE 2, a conduit 53 connects the outputpassageway 23 with a hydraulic motor 54, which performs the work. Fromthe hydraulic motor 54, the exhaust fluid flows by way of a conduit 55to a sump 56. The sump 56 is connected by way of a conduit 57 with theintake passageway 22 of the variable displacement pump. It will beunderstood at this point, that drainage from the pump and also from thetorque control apparatus is conducted to the sump 56. In order toprotect the apparatus from accidental overloading, the pressure conduit53 includes a pressure relief valve 58, which is connected by way of aconduit 59 to the sump 56. The relief valve 58 is conventional and isarranged to bypass the fluid from the pressure conduit 53 to the sump inthe event that the hydraulic motor 54 becomes overloaded, thereby toprevent damage to the equipment.

As noted earlier, the displacement of the variable displacement pump, interms of volumetric output, is determined by the angulation of the swashplate 28, which is mounted for rocking motion with respect to thetrunnions 32. In other words, when the plane of the swash plate isdisposed at right angles to the axis of the drive shaft 15, the pistons17 remain stationary, and as the plane of the swash plate 28 isprogressively inclined, then the pistons are reciprocated within thecylinder barrel to an extent determined by the inclination of the swashplate. The volumetric displacement of the pump from zero to maximum isdetermined by the torque control apparatus of the invention, aspreviously indicated at 2.

The swash plate is interconnected with the torque control apparatus 2 byan arm 60 (FIGURES 2 and 4). Arm 60 projects upwardly from the swashplate at the axis of tilting motion of the swash plate, as provided \bythe trunnions 32-32. The outer or swinging end of arm 60 includes anactuating head portion 6-1 (FIGURES 5 and 6) which is interconnectedwith the torque control apparatus.

Torque control apparatus As noted earlier, the torque control apparatusof this invention regulates, in an automatic manner, the output of pump1 in terms of volumetric displacement and pressure. By way of example,if the load on the hydraulic motor 54 (FIGURE 2) increases to an extentwhich normally would tend to overload the power motor of pump 1, thenthe torque compensator 2 shifts the swash plate 28 in a direction todecrease the stroke of the pistons 17, so as to decrease thedisplacement of the pump, while at the same time increasing the pressuredelivered by way of the ouput passageway 23 to the motor 54. On theother hand, if the load on the hydraulic motor 54 decreases,

then the torque compensator 2 shifts the swash plate 28 in a directionto increase the stroke of the pistons 17, thereby increasing thevolumetric output of hydraulic fluid by way of the output passageway 23so as to increase the speed of the hydraulic motor 54 with aproportionate decrease in torque.

As explained later in detail, the torque compensating apparatus 2(FIGURES 5 and 6) is adjustable so as to enable the user to regulate theapparatus as required by the specific operating conditions of hisequipment. In other words, the apparatus 2 may be adjusted to provide arelatively high volume output at correspondingly lower pressure for awork load which requires relatively high speed operation of thehydraulic motor 54, or it can be adjusted to provide higher operatingpressures at proportionately lower volume if the equipment so requires.

As shown generally in FIGURES 1-3, the torque control apparatus 2resides within a cylindrical cross bore 62 machined in the intermediatesection 4 of the pump housing. As explained later in detail, the torquecontrol apparatus 2 is actuated in response to back pressure which isdeveloped in the pressure conduit 53 (FIGURE 2) which leads from theoutput passageway 23 to the hydraulic motor 54. The several passagewayswhich interconnect the pump, With the compensating apparatus comprisebores which are machined directly into the castings which form theintermediate housing section 4 and the head 18. These passageways aredisclosed diagrammatically in FIGURES 11-13 in the form of conduits, asdescribed below.

Described generally, the head 18 is bored as at 63 (FIGURE 1) to providea pressure passageway com municating with the output passageway 23. Theintermediate section 4 of the pump housing is also bored to provide apassageway 64 which registers with the passageway 63. Passageway 64, inturn, registers with a passageway 65 formed in a collar 66, which formsa part of the torque control apparatus 2. For simplicity, the severalbores 63, 64 and 65 are indicated at A in FIGURE 1 and also in FIGURES11-13. The passageway A (section 65) communicates with the shiftablespool of the pilot valve, as described later.

From the pilot valve, hydraulic fluid is advanced by way of a passageway67 (FIGURE 1) formed in the collar 66. Passageway 67 registers with apassageway 68 formed in the intermediate section 4 and leading to thestroke control piston, which also forms a part of the toque controlapparatus. For convenience, the passageways 67 and 68 are indicated at Bin FIGURE 1 and in the diagrammatic FIGURES 11-13.

Referring to FIGURES 1; and 6, the collar 66, which forms a part of thetorque control apparatus, is attached to the end portion of theintermediate section 4. A cap 72 having a flange T3 is secured by screws74 to the end of the collar 66, the screws 74 passing through collar 66into section 4. The collar 66 and the cap 72 include bores 75 and 76which are concentric with the cross bore 62 of the intermediate housingsection 4.

As detailed in FIGURES 5, 7, and 10, the torque control apparatusincludes an outer ported sleeve, indicated generally at 77, mounted inthe bore 75 of collar 66. The outer end portion of sleeve 77 includes "ahead portion 78 confined in the bore 76 of cap 72, and includes athreaded end portion 80 engaging a screw threaded bore 81 formed withinthe cap 72. The outer ported sleeve 77 is locked in its adjustmentposition by a nut 82 screwed upon its threaded end portion 80. and inclamping engagement with the end of cap 72. The cap 72 includes anannular groove in which is seated a seal ring 70 embracing the headportion 78 to prevent leakage of hydraulic fluid. A similar seal ring 71also seated in an annular groove, seals the cap 72 with respect to thecollar 66.

As explained later in detail, an inner, pilot valve sleeve, indicatedgenerally at 83, is adjustably mounted within the outer ported sleeve 77(FIGURES 6, 7 and A pilot valve spool, indicated generally at 84, ismounted for axial motion within the bore 85 of the pilot valve sleeve 83and controls the admission of hydraulic fluid under pressure to thestroke control piston, indicated generally at 86 in FIGURES 5 and 6. Theaxial position of the pilot valve sleeve 83 regulates the setting ofpump 1 (in terms of displacement and output pressure) in response to therequired operating characteristics (FIG- URES 7 and 10).

For adjustment purposes the outer end of the adjustable pilot valvesleeve 83 includes a spherical head portion 87 confined in a sphericalcavity 88 formed in the end portion of an adjustment screw 90. Theadjustment screw 90 is threaded into a bore 91 formed in the end portion80 of the outer ported sleeve 77. A lock nut 92 is threaded upon the endportion of the adjustment screw 90 and is engaged against the end of theportion 80 to lock the inner pilot valve sleeve 83' in its adjustedposition.

It will be noted at this point, that the collar 66 includes an annulargroove 93 communicating with the pressure passageway A and a secondannular groove 94 communieating with the control passageway B. Ingeneral, the annular groove 93 supplies hydraulic fluid at outputpressure from the output passageway 23 to the pilot valve spool '84 soas to shift the spool in response to back pressure. The spool, inresponse to its shifted position, supplies fluid pressure (passageway B)to the stroke control piston 86 which acts upon the head 61 of arm 60 soas to regulate the angular position of the swash plate 28 in response toback pressure.

Briefly, under minimum back pressure, the apparatus shifts the actuatingarm 60 to the maximum stroke position, as shown in FIGURES 5 and 6, soas to provide maximum pump displacement at minimum pressure. As backpressure increases, the pilot valve spool 84 responds by transmittingadditional fluid under pressure to the stroke control piston 86-,thereby to shift the arm 60 in the direction indicated by the arrow(FIGURES 5 and 6) so as to decrease the stroke and correspondinglyincrease the pump output pressure.-

The pilot valve spool 84 is normally biased toward the right (FIGURES 6,7 and 10) by a compression-type pilot valve spring 95 seated against thehead 96 formed on the end of the valve spool. The spring 95 is held inalignment with the valve spool by a tapered spur 97 which projectsoutwardly beyond the head 96. The opposite end of the valve spring 95 isseated against the closed end 98 of a floating hat-shaped sleeve 100.Sleeve 100 includes a flange 101 which provides a stop engageable with acap 102 seated at the end of the outer ported sleeve 77.

A compression-type arm biasing spring 103 (FIGURES 6, 7 and '10) has oneend seated against the flange 101 of sleeve 100. The arm biasing spring103 presides within a spring guide 104 and its opposite end is seatedagainst the closed end 105 of spring guide 104. The spring guide 104 isin the form of a cylindrical sleeve slidably confined in the cross bore62, and its closed end 105 is in bearing engagement with the head 61 ofthe swash plate arm 60.

The stroke control piston 86 engages the opopsite side of head 61(FIGURES 6, 11, 12 and 13), opposing the spring guide 104, such thatthere is created a biasing action between the spring 103 and strokecontrol piston 86. The stroke control piston 86 is slidably confined ina second section 106 of cross bore 62, and is generally alignedtherewith but of smaller diameter. The end of cross bore 106 includes aclosure cap 107 having a seal ring 108 seated in an annular groove andunder compression within bore 106. The closure cap includes a flange 110and is secured in place by screws 111 passing through flange 110.

In order to supply hydraulic pressure from the control passageway B, thecross bore 106 includes an annular groove 112 in communication withpassageway B and surrounding the stroke control piston 86 (FIGURE 6).From the annular groove 112 the hydraulic fluid pressure is transmittedby way of the longitudinal grooves 113 to the end of piston 86. Thepiston 86 may include radial openings 114 leading from the grooves 113to its internal bore 115 to allow the fluid pressure to act upon themajor diameter of the piston.

As best shown in FIGURES 710, the shiftable spool 84 of the pilot valveincludes three lands indicated at 116, 117 and 118 slidably interfittingthe bore 85 of the adjustable valve sleeve 83. The spool 84 includesnecked portions 120 having a diameter smaller than the lands to providethe valving action, as explained later. When the pump 1 is at rest, orrunning at low pressure with maximum displacement, the valve spool 84assumes the position shown in FIGURES 6, 7 and 11. In this position,hydraulic fluid from the pump flows by way of passageway A through theannular groove 93 and through the ports 119 of the outer ported sleeve77 (FIGURE 7). From ports 119, the fluid passes to the relief groove 121of the outer ported sleeve 77. From the relief groove 121, the hydraulicfluid passes into ports 122 of the inner pilot valve sleeve 83. Fromports 122, the hydraulic fluid passes into the bore '85 of valve sleeve83 between the lands 117 and 118 of the valve spool 84.

As explained later with reference to FIGURES 7-10 the land 118 of valvespool 84 includes relief areas 123 (FIGURE 8). The relief areas permitthe fluid pressure from port 122 to pass through the bore 85 to therearward end of spool 84, as indicated by the arrow in FIGURE 7. Thispermits the back pressure to act upon the full diameter of the shiftablevalve spool 84 (the land 117 being sealed with reference to the bore 85)thereby urging the valve spool 84 toward the left against its biasingspring 95.

In order to drain hydraulic fluid from the pilot valve, the land 116, atthe forward end of valve spool 84 in cludes relief areas 124 (FIGURE 9)similar to a relief area 123 of land 118. Hydraulic fluid thus passesfrom the pilot valve sleeve 83, through the aperture 125 (FIG- URE 6) ofthe spring guide 104 to be returned to the circulatory system of thepump. The drain passageway is indicated diagrammatically at 127 inFIGURE 2, leading to the sump 56 of the hydraulic system.

As explained later in detail, back pressure in conduit 53 and passagewayA acts upon the pilot valve spool 84, tending to shift the spool towardthe left (FIGURES 10 and 12) counter to the action of pilot valve spring95. As the spool is moved toward the left, the land 117 uncovers theports 126 of inner valve sleeve 83, thus providing communication fromthe ports 126 to the annular passageway 94 and passageway B, whichcommunicates with the stroke control piston 36.

Operation In order to adjust the output pressure of the pump, the innervalve sleeve 83 is shifted axially with respect to the outer portedsleeve 77, thus changing the relative position of the ports 122 and 126with respect to the lands 116 and 117. To increase the output pressure,the lock nut 92 is loosened and the adjustment screw 90 is rotated in adirection to shift the inner valve sleeve 83 toward the left, as shownin broken lines in FIGURE 7, thus increasing the axial motion which mustbe imparted to the valve spool 84 under back pressure. Since the pilotvalve spool 84 is biased by the valve spring 95, the back pressure(outlet passageway 23 and passageway A) neces sarily is increased beforethe pilot valve spool 84 is shifted axially a sutficient distance touncover the ports 126. As noted above, ports 126 deliver the hydraulicpressure to stroke control piston 86 so as to decrease displacement andincrease pump pressure. On the other hand, when the adjustment screw 90is rotated in a direction to shift the pilot valve sleeve 83 toward theright, then the required axial travel of the pilot valve spool touncover ports 126 is reduced. As a consequence, the back pressure ofoutlet passageway 23 and passageway A necessary to shift spool 84 isreduced, so as to decrease the maximum output pressure of the pump andto increase its displacement.

As noted earlier, the actuating arm 60 of swash plate 28 automaticallyassumes the position of FIGURES and 6 when the pump is shut down or whenthere is a minimum load on the hydraulic motor 54 (FIGURE 2), thusproviding maximum pump displacement at low pressure. As the load on thehydraulic motor 54 increases, back pressure in output passageway 23 andpressure passageway A correspondingly increases. As shown by the arrow Cin FIGURE 7, the'fluid pressure from passageway A and port 122 acts uponthe full diameter of land 117 by operation of the relief areas 123(FIGURE 8) thus tending to shift the pilot valve spool 84 toward theleft and causing land 117 to uncover port 126, as noted above. As fluidpressure is transmitted to-the stroke con trol piston 86, the piston andswash plate control arm 60 are shifted toward the right, as previouslyindicated by the arrows in FIGURES 5 and 6. This motion tends tocompress the coil spring 95 (by operation of spring guide 104 and armbiasing spring 103), thereby tending to shift the pilot valve spool 84back toward the right in a direction to cover port 126. Thus, thecoaction between the pilot valve spool 84 and stroke control piston 86provides, in eflfect, a servo-motion leading to a state of balancebetween the stroke control piston 86 and pilot valve spool 84. Otherwiseexpressed, motion of the pilot valve spool toward the left (FIGURES l0and 12) causes a corresponding mot-ion of the stroke control piston toward the right, thus tending to shift the valve spool back toward theright through operation of the valve spring 95.

It will be understood that the right hand motion (FIG- URE 13) of theactuating arm 60 reduces the piston stroke and displacement of the pumpand increases output pressure so as to compensate for the increased loadon the hydraulic motor 54. As the torque control apparatus reacts to theload resistance, as noted above, a state of equilibrium is establishedbetween the pump and motor, as determined by the setting of theadjustment screw 90. In other words, the spool is balanced by the forceof the compressed spring acting in one direction and by the force ofhydraulic pressure acting upon the spool in the opposite direction.

When the pilot valve spool 84 is thus balanced, the land 117 blocks olfthe ports 126 to prevent further admis sion of fluid to the strokecontrol piston 86. However, a decrease in back pressure will cause thespring 95 to shift spool 84 toward the right. This motion permits fluidpres sure to pass from stroke control piston 86 and passageway B,through ports 126 and through the relief areas 124 of land 116, and todrain by way of cross bore 62 and aperture 125 (drain 127FIGURE 2). Thedrainage flow is indicated by the arrow D in FIGURES 2 and 13. As aconsequence, the pilot valve spool floats substantially in a state ofbalance and responds immediately to any change in the load resistance ofhydraulic motor 54 (and back pressure) to control the stroke and outputpressure of the pump.

As the load on the hydraulic motor 54 approaches the maximum for whichthe torque control apparatus is ad justed, the flange 101 of thehat-shaped sleeve comes into contact with the cap 102 (FIGURE 6). Underthis condition, the actuating arm 60 of the swash plate is in theposition of intermediate stroke and maximum pressure. As noted earlier,the arm biasing spring 103 is formed of spring wire having a diameterseveral times greater than the valve control spring 95. Under normaloperation, with the hat-shaped sleeve 100 floating, the motion impartedby the stroke control piston to arm 60 produces a deflection of both theheavy spring 103, and the control spring 95, thus raising the bias loadof spool 84, and the pump discharge pressure. However, when the valvecontrol sleeve 100 reaches its limit of motion, then further motion ofthe actuating arm 60 results in further compression of the spring 103only. Discharge pressure of the pump then remains constant at minimumstroke.

As noted earlier, the pump 1 is also adapted to be used as a hydraulicmotor. In the present example, hydraulic pressure may be transmitted tothe motor by way of the intake passageway 22 so as to act upon thepistons 17 of cylinder barrel 9, thereby imparting rotary motion to thebarrel by the reaction of the pistons against the swash plate 28. Thehydraulic fluid in this case is discharged from the motor by way of theoutlet passageway 23. The shaft 15 is thus rotated by the cylinderbarrel 9 to drive the element which is connected to the shaft 15.

Having described my invention I claim:

1. A torque control apparatus for a hydraulic power unit, said powerunit having a pressure passageway and having a series of displacementpistons, said power unit having a movable element adapted to be shiftedin a fiat plane in response to back pressure in the pressure passagewayto control the stroke of said pistons and the displacement of the powerunit, said control apparatus comprising:

an axially shiftable stroke control pistion connected to the movableelement of the power unit and adapted to shift the same for increasingor decreasing the stroke of said pistons and thereby the displacement ofthe power unit;

disposed in axial alignment with said stroke con- 1 l trol piston andengaging said movable element in opposition to said stroke controlpiston;

a compressible spring element interposed between the axially shiftablevalve spool and movable element, adapting the valve spool to act uponthe movable element through said spring element;

said power unit including means providing hydraulic Communicationbetween said pressure passageway and said shiftable valve spool, wherebythe valve spool is shifted toward said movable element in response toback pressure in said pressure passageway to urge the movable elementthrough the compress ible spring element toward said stroke controlpiston;

said axially shiftable valve spool adapted to transmit hydraulicpressure in response to said movement of the valve spool to said strokecontrol piston in a direction to force the same toward the movableelement opposite to the force exerted by said valve spool and springelement, whereby the axially shiftable valve spool and axially shiftablestroke control piston bias one another against said movable ele ment toprovide a servo action and thereby a balanced relationship to hold themovable element at a position providing a given piston stroke inresponse to a give back pressure in said pressure passageway.

2. A torque control apparatus for a hydraulic power unit, said powerunit having a pressure passageway and having a series of displacementpistons, said power unit having a casing including a cross bore andhaving a movable element adapted to be shifted in a flat plane inresponse to back pressure in the pressure passageway to control thestroke of said pistons and thereby the displacement of the power unit,said torque control apparatus comprising:

an axially shiftable stroke control piston slidably confined in one endportion of said cross bore, said piston engaging the movable element ofthe power unit and adapted to shift the same for controlling the strokeof the pistons of the power unit;

a pilot valve residing in an opposite end portion of said cross bore inaxial alignment with said stroke control piston;

an axially shiftable pilot valve spool disposed in said pilot valve inaxial alignment with said stroke control piston and engaging saidmovable element on the side opposite said stroke control piston;

a compressible spring element interposed between the axially shiftablevalve spool and movable element, adapting the valve spool to act uponthe movable element to the said spring element;

said power unit including means providing hydraulic communicationbetween said pressure passageway and said shiftable valve spool, wherebythe valve spool is shifted toward said moveable element in response toback pressure in said pressure passageway:

said axially shiftable valve spool adapted to transmit hydraulicpressure to said stroke control piston to force the piston toward themovable element in a direction opposing the shiftable valve spool,whereby the axially shiftable valve spool and axially shiftable strokecontrol piston bias one another against said movable element and therebyprovide a servo action, thereby to hold the same at a given strokecontrol position in response to a given back pressure in said pressurepassageway.

3. A torque control apparatus for a hydraulic power unit, said powerunit having a pressure passageway and having a series of displacementpistons, said power unit having a casing including a cross bore andhaving a movable element adapted to be shifted in a flat plane throughan arcuate path in response to back pressure in the pressure passagewayto control the stroke of said pistons and thereby the displacement ofthe power unit, said torque control unit comprising:

an axially shiftable stroke control piston slidably confined in one endportion of said cross bore, said piston engaging the movable element ofthe power unit and adapted to shift the same axially for controlling thestroke of the pistons of the power unit;

a pilot valve sleeve residing in an opposite end portion of said crossbore in axial alignment with said stroke control piston, said pilotvalve sleeve including ports communicating with said pressure passagewayand with said stroke control piston;

an axially shiftable pilot valve spool confined in said pilot valvesleeve generally in alignment with said stroke control piston andengaging said movable element on the side opposite said stroke controlpiston;

means for adjusting said pilot valve sleeve axially relative to thevalve spool;

said power unit including means providing hydraulic communicationbetween said pressure passageway and the ports of said pilot valvesleeve;

said ports adapting the valve spool to be shifted toward said movableelement in response to back pressure in said pressure passageway;

a land on said axially shiftable valve spool, said land being acted uponby hydraulic pressure from the ports of the valve sleeve in a directionto shift the valve spool toward the movable element, said land, uponbeing shifted toward the movable element, adapted to transmit hydraulicback pressure from the ports of the valve sleeve to the stroke controlpiston to urge the piston in a direction opposing the shiftable valvespool, whereby the axially shiftable valve spool and axially shiftablestroke control piston bias one another axially against said movableelement and providing a servo action, thereby to hold the same at agiven stroke control position in response to a given back pressure insaid pressure passageway as determined by the adjustment of the pilotvalve sleeve.

4. A torque control apparatus in accordance with claim 3 in which thereis provided an outer sleeve confined in a fixed position in the crossbore generally in alignment with the stroke control piston, said outersleeve having ports in communication with the pressure passageway of thepower unit and with the stroke control piston, said pilot valve sleevebeing mounted within said outer sleeve for axial adjustment relative tothe outer sleeve, with the ports of the outer sleeve and valve sleevemaintaining communication with saidpower passageway and with said strokecontrol piston.

5. A torque control apparatus for a hydraulic power unit, said powerunit having a pressure passageway and having a series of displacementpistons, said power unit having a casing including a cross bore andhaving a movable element adapted to be shifted in a flat plane throughan arcuate path to control the stroke of said pistons and thereby thedisplacement of the power unit, said torque control unit comprising:

an axially shiftable stroke control piston slidably confined in one endportion of said cross bore, said piston engaging the movable element ofthe power unit and adapted to shift the same for controlling the strokeof the pistons of the power unit;

a pilot valve residing in an opposite end portion of said cross bore inaxial alignment with said stroke control piston;

an axially shiftable pilot valve spool disposed in said pilot valvegenerally in axial alignment with said stroke control piston andengaging said movable element on the side opposite said stroke controlpiston;

a first compressible spring element interposed between theaxially'shiftable valve spool and movable element, adapting the valvespool to act upon the movable valve element through said compressiblespring element,

a second compressible spring element concentric with the first springelement and having an end seated against the movable element of thepower unit;

means connecting the opposite end of said second spring element to thefirst spring element, whereby the motion of the movable element of thepower unit is transmitted through said first and second spring elementsto the pilot valve spool;

said power unit including means providing hydraulic communicationbetween said pressure passageway and said shiftable valve spool, wherebythe valve spool is shifted through the first spring element to ward saidmovable element in response to back pressure in said pressurepassageway;

said axially shiftable valve spool adapted to transmit hydraulicpressure to said stroke control piston to force the same toward themovable element in a direction opposite to the force exerted by saidvalve spool, whereby the axially shiftable valve spool and axiallyshiftable stroke control piston bias one another against said movableelement and provide a servo action and thereby a balanced relationshipto hold the movable element at a given position to provide a givenpiston stroke in response to a given back pressure in said pressurepassageway.

6. A torque control apparatus in accordance with claim in which there isprovided a sleeve element seated against the end portion of said firstcompressible spring element opposite the pilot valve spool and slidablyconfined in the cross bore, said sleeve element having an exteriorflange formed thereon, said sleeve element telescopically interfittingsaid second compressible spring element, the end of the second springelement opposite the movable elements of the movable element aretransmitted through said second compressible spring element to the saidsleeve and through said first spring element to the pilot valve spool.

7. A torque control apparatus for variable displacement hydraulic pump,said pump having a casing including an intake and an output passageway,said casing including a cross bore and having a pressure passagewaycommunicating with a first end portion of said cross bore, said casinghaving a control passageway connecting said first end portion of thecross bore to a second end portion thereof, said pump casing including aplurality of pistons, a tiltable swash plate adapted to control thestroke of said pistons, said swash plate including an actuating arm forcontrolling the tiltable motion of the swash plate, said torque controlapparatus comprising:

a stroke control piston slidably confined in-the second end portion ofsaid cross bore, said piston engaging the actuating arm of the swashplate and adapted to shift the swash plate for controlling the stroke ofthe pump pistons;

a pilot valve including an axially shiftable valve spool disposed in thefirst end portion of the cross bore generally in alignment with saidstroke control piston;

an adjustment screw threaded through an end portion of said casing; i

a ball and socket joint connecting the adjustment screw to said axiallyshiftable valve spool and adapted'to shift the same axially in forwardor reverse directions in response to rotation of said adjustment screw;

said pressure passageway adapted to transmit hydraulic fluid pressure tothe first end portion of the cross bore adjacent the end of said valvespool to force the valve spool toward said actuating arm;

said shiftable valve spool adapted to transmit hydraulic pressure tosaid control passageway in response to motion of the valve spool towardsaid actuating arm;

said control passageway communicating with the second end portion of thecross bore adjacent the end of said stroke control piston and adapted toforce the stroke control piston toward the actuating arm in a directionopposing the shiftable valve spool, whereby the valve spool and strokecontrol piston bias one another axially against said actuating arm tohold the swash plate at a given stroke control position in response to agiven back pressure in said output passageway. 8. A torque controlapparatus for a variable displacement hydraulic pump, said pump having acasing including an intake and an output passageway, the casing having across bore and having a pressure passageway connecting the outputpassageway with a first end portion of the cross bore, the casing havinga control passageway connecting said first end portion of the cross boreto a second end portion of the cross bore, said pump having a movableelement adapted to be shifted in a fiat plane through an arcuate path tocontrol the hydraulic displacement of the pump, said torque controlapparatus comprising:

a shiftable displacement control piston mounted in the second endportion of said cross bore, said piston engaging the movable element ofthe pump and adapted to shift the same for controlling the displacementof the pump;

a pilot valve sleeve residing in the first end portion of I said crossbore generally in alignment with said displacement control piston, saidpilot valve sleeve including ports communicating with said pressurepassageway and with said control passageway of the pump casing;

an axially shiftable pilot valve spool confined in said pilot valvesleeve generally in alignment with said displacement control pistonandengaging the movable element of the pump on the side opposite saiddisplacement control piston;

means for adjusting said pilot valve sleeve axially relative to thevalve sleeve, said pressure passageway of the pump casing transmittinghydraulic back pressure from said output passageway through the ports ofsaid pilot valve to said shiftable valve spool;

said adjustment means comprising an adjustment screw threaded through anend portion of said casing and having a socket formed in the inner endportion thereof;

said pilot valve spool having a spherical head interfitting said socketand adapted to be shifted axially in forward or reverse directions inresponse to rotation of the adjustment screw;

a land on said valve spool acted upon by said back pressure whereby thevalve spool is urged hydraulically toward the movable element of thepump in response to the back pressure of the output passageway;

said land of the axially shiftable valve spool adapted to transmithydraulic pressure from the ports of the valve sleeve through thecontrol passageway of the casing to the second end portion of the crossbore, whereby the back pressure acts upon the displacement controlpiston to force the same toward said movable element of the pump,whereby the axially shiftable valve spool and axially shiftable strokecontrol piston -bias one another against opposite sides of the movableelement to hold the same at a given displacement position in response toa given back pressure in said output passageway'and pressure passagewayas determined by the adjustment of the pilot valve sleeve.

9. A torque control apparatus in accordance with claim 8 in which saidpressure passageway and ports of the valve sleeve communicate with oneside of said land to urge the valve spool toward the movable element andin which the end of the valve spool adjacent said movable element isprovided with a second land havingrelief areas, whereby a drop in thehydraulic back pressure transmitted by the pressure passageway adaptsthe displacement control piston and movable element of the pump to shiftin a direction opposing the shiftable valve spool, said second landadapting the hydraulic pressure to be exhausted from the 1 5 axiallyshiftable displacement control piston'through the control passageway andthe relief areas of the second land and from the valve sleeve asdetermined by the adjustment of the pilot valve sleeve.

References Cited by the Examiner UNITED STATES PATENTS 2,379,546 7/1945Snader 103-162 Febvre 103-162 Davis l03-l62 Lambeck 103-38 Wahlmark103--162 SAMUEL LEVINE, Primary Examiner.

LAURENCE V. EFNER, Examiner. J. C. MUNRO, Assistant Examiner.

1. A TORQUE CONTROL APPARTUS FOR A HYDRAULIC POWER UNIT, SAID POWER UNITHAVING A PRESSURE PASSAGWAY AND HAVING A SERIES OF DISPLACEMENT PISTONS,SAID POWER UNIT HAVING A MOVABLE ELEMENT ADAPTED TO BE SHIFTED IN A FLATPLANE IN RESPONSE TO BACK PRESSURE IN THE PRESSURE PASSAGEWAY TO CONTROLTHE STROKE OF SAID PISTONS AND THE DISPLACEMENT OF THE POWER UNIT, SAIDCONTROL APPARATUS COMPRISING: AN AXIALLY SHIFTABLE STROKE CONTROL PISTONCONNECTED TO THE MOVABLE ELEMENT OF THE POWER UNIT AND ADAPTED TO SHIFTTHE SAME FOR INCREASING OR DECREASING THE STROKE OF SAID PISTONS ANDTHEREBY THE DISPLACEMENT OF THE POWER UNIT; A PILOT VALVE INCLUDING ANAXIALLY SHIFTABLE VALVE SPOOL DISPOSED IN AXIAL ALIGNMENT WITH SAIDSTROKE CONTROL PISTON AND ENGAGING SAID MOVABLE ELEMENT IN OPPOSITION TOSAID STROKE CONTROL PISTON; A COMPRESSIBLE SPRING ELEMENT INTERPOSEDBETWEEN THE AXIALLY SHIFTABLE VALVE SPOOL AND MOVABLE ELEMENT, ADAPTINGTHE VALVE SPOOL TO ACT UPON THE MOVABLE ELEMENT THROUGH SAID SPRINGELEMENT; SAID POWER UNIT INCLUIDNG MEANS PROVIDING HYDRAULICCOMMUNICATON BETWEEN SAID PRESSURE PASSAGEWAY AND SAID SHIFTABLE VALVESPOOL, WHEREBY THE VALVE SPOOL IS SHIFTED TOWARD SAID MOVABLE ELEMENT INRESPONSE TO BACK PRESSURE IN SAID PRESSURE PASSAGEWAY TO URGE THEMOVABLE ELEMENT THROUGH THE COMPRESSIBLE SPRING ELEMENT TOWARD SAIDSTROKE CONTROL PISTON; SAID AXIALLY SHIFTABLE VALVE SPOOL ADAPTED TOTRASMIT HYDRAULIC PRESSURE IN RESPONSE TO SAID MOVEMENT OF THE VALVESPOOL TO SAID STROKE CONTROL PISTON IN A DIRECTION TO FORCE THE SAMETOWARD THE MOVABLE ELEMENT OPPOSITE TO THE FORCE EXERTED BY SAID VALVESPOOL AND SPRING ELEMENT, WHEREBY THE AXIALLY SHIFTABLE VALVE SPOOL ANDAXIALLY SHIFTABLE STROKE CONTROL PISTON BIAS ONE ANOTHER AGAINST SAIDMOVABLE ELEMENT TO PROVIDE A SERVO ACTION AND THEREBY A BALANCEDRELATIONSHIP TO HOLD THE MOVABLE ELEMENT AT A POSITION PROVIDING A GIVENPISTON STROKE IN RESPONSE TO A GIVE BACK PRESSURE IN SAID PRESSRUEPASSAGEWAY.